Satellite navigation systems are widely-used for determining the location of an earth-based receiver. The receiver calculates a distance, referred to as a “pseudorange”, to a satellite, based on a measured time-of-flight of a received signal and a known speed of the signal, i.e. the speed of light. Signals must be received from at least four satellites in order to perform triangulation and calculate a local clock offset at the receiver.
A common source of interference in conventional navigation systems is multipath interference, in which signals are reflected from objects such as buildings before reaching the receiver. Multipath interference is illustrated in FIG. 1, which shows a receiver 100 receiving a direct line-of-sight signal 122 from a satellite 120. The receiver 100 also receives multipath signals 124, 126 which have been reflected off nearby buildings 110, 112. The multipath signals 124, 126 have travelled further than the line-of-sight signal 122, and hence cause the receiver 100 to incorrectly calculate the distance to the satellite 120. Also, because the multipath signals 124, 126 are delayed copies of the line-of-sight signal 122, they can cause interference with the line-of-sight signal 122 at the receiver 100. Multipath effects therefore degrade signal quality and can reduce positioning accuracy.